Production of leather



ing leather.

Patented June ll, 1935 A If rnonocrroxoa neairnnn Q Y Gorge .n. rii eiQaiii ter a i N. 1

No Drawing, Application Mayne; 1931,

s riarnas mza 1 4 Clai s. (cl. 1'49--3 This invention relates to processes oflprepar:

More specifically, it is directedto a novel treatmentof skins preliminary to the actual tanning operation, whichcontributes to the production of leather of excellent quality. I

As far as I am aware, no one-up to thepresent time has'beencommercially successfulin producing tough, pliable leather having thejgrain left thereonfiby any process employing formaldehyde.

The leather resulting from previous attempts'has been hardand' brittle. Accordingly, an object. of the present invention is to process using formaldehyde which will produce grain leather acceptable to the trade. It is to be understood, however,that the: instant process is excellently "suitable for the production of leather from all classes of skins, including lizard and snake skins, shearlings and furs.

Other and further objects of the present invention will be apparent to those skilled in the art upon studying the present specification and claims. I

According to methods now in use, skins as received at the cannery pickled in sulfuric acid and sodium bicarbonate, borax, whiting; etc., to neutralize the strong acid prior. to the actual tanning operation. According to salt, are treated with the present invention andjconstituting an important feature thereof, the strong acid is not neutralized directly but is converted into or replaced by a weak organic acid. which is then neutralized to a pH number of about 5.2 to 6.0 by the addition of an agent such as sodium bicarbonate or borax. The strong vacid is removed by treating the skins with a soluble salt of a weak organic acid, such as an alkali metal salt of acetic, oxalic, lactic, tartaric, citric, formic and other such weak acids, whichsalt reacts weak organic tanning or'tawing is effected by the use of an aldehyde. And further, the best results are obtained when the formaldehyde tannageis of the particular nature hereinafter described in detail.

This particular tanning operation isperformed bath composed of a sperm; The skins provide a tannery' 1:

1 acetate and about 20 to small additional raises the pfltnuniber by subjecting flthe neutralized skins to a treat-.

ment at a" slightly-elevated"temperature .with a solution of formaldehyde,

.Glauberlsnsalt, borax and a. substance whichassists the formaldehyde in-entering-theskins, such as a sodijumsoap or asmall amount of emulsified olive, cocoanut, or sperm oil; or. mixtures of sul' phonated- ,oils; preferably castor, cocoanut and are then washed, and bleached, ifnecessary.

1;; The novelfat liquoring treatment iwhich, fol- -'lows,-though quite important 11:0 thesuccessful production of some. leathers. such asigraina leather,

" is notof so much importance to others. grain leather is treated, it :is heated at a V slightly When elevatedtemperature in a bath containing a sulphonatedmixture of sperm and cocoanut oils.

When suedes are treated, sulphonated castor oil l is added to the bath. "After a treatment with weak acetic acid and a washing operation, the skinsare ready for finishing; V

Other aldehydes than formaldehyde may be successfully employed, for instance, acrolein.

As an example of the complete process of the present invention, a typical run in which'doeski'ns are tanned is herein set out, the quantities of substances. used being those'amounts employed per one hundred pounds of pickled skins. v The pickled skins as received; which contain sulphuric acid, are .fleshed and degreased, as,

for example,,with kerosene, and then soaked and agitatedin a drum having therein a water solu' tion containing about 5 to 6 pounds of sodium 24 pounds. of Glau'bers salt for each twenty gallons of water. The agi-f tation is continued for a period of about a hali v hour at a temperature F.

in the neighborhood of In some cases where the'skins contain an unusual 'or excess amount of sulphuric acid, a somewhat larger amount of sodium acetate should be used. Also for grain leather skins the amount of Glaubers salt above indicated should be substantially increased even up to fifty pounds.

To the drum may then beadded 2 to 6 pounds. of 56% acetic acid in a solution containing a quantity of Glaubers salt,.after which the soaking and agitating is continued for aboutanother half hour., The solution now has a pH value of approximately152.

Next, the acetic acid'solutionis neutralized by adding about 2 to 3 pounds of bicarbonate of soda, or the equivalent in borax, in solution in waterxcontaining additional Glaubers, salt. This.

of the solution to approxie dehyde.

mately 5.5. After a. run of about a half hour, with the temperature still about 80 F., the skins are slatted off and the liquid drained away.

Then the actual tanning operation begins, A solution containing about 6 to 7 pounds of formaldehyde solution) and 3 to 5 pounds of borax is then added to the drum and run for about an hour at about F. Additional acetic acid is then addedto the tanning solution. This lowers the pH value by producing boric acid. To the solution is then added an agent which produces a colloidal condition in the tanning solution which in turn aids the penetration of the formal- In the present case, this agent is a sodium soap containing, for example, 88% mentral soap made from cocoanut oil and white tallow in about equal proportions,

and about 10% of Glaubers salt. The contents are then heated to a boiling temperature and cooled to about F. in about an hour, after which a heating at temperatures gradually increasing to 140 F. over a period of about two hours is effected. This heating may be carried out by running for an hour during a temperature increase from 120 to 1",, running at 130 F. for a half hour, and

at temperatures increasing to 'F. for an additional half hour, at which time the tanning is complete. The skins are next washed and then bleached if necessary.

The following fat liquoring process has been found excellently suitable for the production of soft and pliable leather 'from the skins tanned by the foregoing process. grain leather, about 125 F. taining about 10 In the treatment of the tanned skins are heated at for a half hour in a drum conpounds 0! a sulphonatedl mixture of equal parts of sperm and cocoanut oils dispersed in water. About 5 pounds of 28% acetic acid dissolved in water is then added gradually to the drum over a period of about a half hour. for about 20 minutes at a temperature of about 100 after which the leather is ready for finishing. p l Having thus described the invention, what is claimed as new and desired to be'secured by Letters Patent is:

1. In the production 0 leather from skins pickled in strong acid of the pickle solution, the step comprising replacing the strong acid in said skins with acetic acid, and then converting the skins into leather by a formaldehyde tannage process.

2. In the production of leather from skins pickled in strong acid, the steps comprising soaking said skins in a solution containing an alkali salt of acetic acid, neutralizing the acid in the skins to approximately pH 5, and converting the skins into leather by treatment in a bath containing formaldehyde and borax.

3. In the production of leather from, skins pickled in strong acid, the steps comprising replacing the strong acid of the pickled solution in the skins with a soluble fatty organic acid, and then converting'the skins into leather by the formaldehyde tannage process.

4. In the process of. producing leather from skins, the steps of treating the skins with a salt of an organic acid together with aquantity of said organic acid, and then converting the skins into leatherrby a formaldehyde tannage process.

. GEORGE R. PENSEL.

The treated leather is next washed 7 

